1. Field of the Invention
The present invention relates to a polymer scale preventive agent useful in polymerization of a monomer having an ethylenically unsaturated double bond, a polymerization vessel for preventing polymer scale deposition, and a process of producing polymer using said vessel.
2. Description of the Prior Art
In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymer deposits on the inner wall surface and so forth in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality of the manufactured polymer; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomer and operators may be exposed thereto, which may cause physical disorders in the operators.
Heretofore, as methods for preventing polymer scale deposition on the inner wall surface and so forth of a polymerization vessel in polymerization of a monomer having an ethylenically unsaturated double bond, methods in which substances exemplified below are coated on the inner wall surface, etc. as a scale preventive agent, have been known.
For example, particular polar organic compounds (Japanese Patent Publication (KOKOKU) No. 45-30343(1970)), a dye or pigment (Japanese Patent Publication (KOKOKU) No. 45-30835(1970), an aromatic amine compound (Japanese Pre-examination Patent Publication (KOKAI) No. 51-50887(1976)) and a reaction product of a phenolic compound and an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 55-54317(1980)) are disclosed.
In the meantime, vinyl chloride polymers obtained by polymerization are required to have a good whiteness. That is, when polymeric products such as vinyl chloride polymers are formed or molded with no addition of a coloring agent, the resulting formed or molded product is colored more or less. This coloration is called initial coloration, which is required to be as low as possible. Specifically, for example, the formed or molded products are required to have an L value according to the Hunter's color difference equation, which is described in JIS Z 8730 (1980), of 70 or more.
The prior art polymer scale preventive agents generally include a great number of colored substances as exemplified typically by the dyes and pigments described in Japanese Patent Publication (KOKOKU) Nos. 45-30835(1970) and 52-24953(1977), the aromatic amine compounds described in Japanese Pre-examination Patent Publication (KOKAI) No. 51-50887(1976), and the reaction products of a phenolic compound and an aromatic aldehyde described in Japanese Pre-examination Patent Publication (KOKAI) No. 55-54317(1980). Presumably, for this, a colored polymer is obtained in suspension polymerization and the like of vinyl chloride, etc. in a polymerization vessel which has a coating comprising the polymer scale preventive agent described above formed on its inner wall. That is, according to measurement of the lightness L described above, the L may be measured to be 65 or less, and coloration is thereby confirmed. Presumably, the coloration is caused by incorporation of components of the coating which has dissolved or peeled into the polymerization mass. Improvement is required for producing a polymer of high quality.
In the U.S. patent application Ser. No. 07/780,464 filed on Oct. 22, 1991 by T. Shimizu et al., now abandoned, is disclosed a polymer preventive agent, as one which is effective in producing polymeric products with a low initial coloration, comprising an N-acylated or N-sulfonylated leucophenothiazine having the general formula: ##STR2## wherein Z is a carbonyl group or a sulfonyl group, R.sup.1 and R.sup.2 may be the same or different and each represent a hydrogen atom, a hydroxyl group or a group having the formula --N(R.sup.4)(R.sup.5) where R.sup.4 and R.sup.5 may be the same or different and each represent a hydrogen atom, an alkyl group or a formyl group, and R.sup.3 is a hydrogen atom, halogen atom, alkyl group, haloalkyl group, alkoxyl group, aryl group or a group having the formula: --N(R.sup.6)(R.sup.7) where R.sup.6 and R.sup.7 may be the same or different and each a hydrogen atom or an alkyl group. In the U.S. patent application Ser. No. 07/705,554 filed on May 24, 1991 by T. Shimizu et al., now U.S. Pat. No. 5,153,281 is disclosed a polymer scale preventive agent, as one which is safe and effective in producing polymeric products with a low initial coloration, comprising a water-soluble basic polysaccharide such as chitosans. The present invention relates to an improvement of the agents described in the U.S. applications above in prevention of polymer scale deposition.